Category Archives: SQL Primary Key Constraint

SQL Primary Key & Constraints

Difference between Primary key and Unique key

By | October 5, 2009

var gaJsHost = ((“https:” == document.location.protocol) ? “https://ssl.” : “http://www.”); document.write(unescape(“%3Cscript src=’” + gaJsHost + “google-analytics.com/ga.js’ type=’text/javascript’%3E%3C/script%3E”)); try { var pageTracker = _gat._getTracker(“UA-11608194-1”); pageTracker._trackPageview(); } catch(err) {} Both Primary key and Unique key enforce uniqueness of the column on which they are defined but still there are some differences between them. The differences are defined… Read More »

Sql server Constraints – Primary Key, Foreign Key, Unique Key, Not Null, Check Constraints

By | August 19, 2009

A constraint is a property that is assigned to a column or a group of columns to prevent incorrect or corrupt data from entering into the tables. These constraints ensure the accuracy and reliability of the data into the tables. Let’s suppose we have two tables Employee and Department whose description is given below:- CREATE… Read More »